This invention relates to a multiplex data processing system including a computer system provided with two or more interconnected processors each having arithmetic and logic units and each capable of operating independently, and, more particularly, to a data processing system wherein a single memory device is commonly used by a plurality of data processing units and wherein a specific job is performed according to the order of priority of the jobs requested.
A complex or multiplex data processing system in which a single memory device is used in common has been developed for the purpose of improving the capability and reliability of a data processing system and for efficiently utilizing system resources such as memory devices and peripheral units.
Where a multiplex data processing system is made up of a plurality of data processing units, the capability of the data processing is increased many times. Actually, however, the processing capability would not be increased so much because such system resources as the memory devices and peripheral units operate concurrently and the low response speed of the software which smoothly administrates the entire system.
The methods of constructing a multiplex data processing system are generally classified into the following two methods. According to one method, a data processing unit for controlling the entire system is connected to other controlled data processing units through a shared memory device and a common bus line. This method is called a hierarchy system. According to the other method, there is no dependent relationship between respective data processing units. This method is termed a non-hierarchy system. In the hierarchy system, since the dependent relationship between controlling and controlled data processing units is distinct, the planning, practicing and evolution of the system are relatively easy. In the hierarchy system, however, the processing capability of the entire system is limited by the queuing in the controlling data processing unit and the processing capability of the controlling data processing unit itself.
In the non-hierarchy system any data processing unit operates independently without being governed by the other data processing units, so that its processing ability is much higher than that of the hierarchy system. However, the non-hierarchy system is not advantageous in that due to a special linkage between respective data processing units, it is often necessary to use a special coupling-release command, for example, a JOIN command or a FORK command. Moreover, as the software or the operating systems of respective data processing units are required to have functions of executing the commands, the computer system becomes complicated and the application programs of the user are adversely affected.